Ataxia-telangiectasia (A-T) is a human autosomal recessive disorder caused by mutations in the gene encoding a protein, termed A-T mutated (ATM). A-T is characterized by cerebellar ataxia, retinal telangiectasia, immunodeficiency, radiosensitivity, infertility, predisposition to malignancies and progressive neuronal degeneration. There is no cure for A-T;hence, current treatments are directed toward alleviating symptoms. Here we propose to achieve targeted gene therapy for A-T, mediated by an HSV/AAV Rep+ hybrid amplicon vector. The transgenes within the amplicon vectors are flanked with adeno-associated virus (AAV) inverted terminal repeats (ITRs) sequences, which in the presence of AAV Rep proteins can achieve a high frequency of integration into the AAVS1 site on chromosome 19 in human cells and in transgenic mouse cells bearing this human sequence. In the proposed studies, we will evaluate integration events into the genome of dividing A-T fibroblasts and post mitotic Atm -/- neurons. We will also elucidate site-specific integration in vivo, in an Atm -/- mouse model bearing human AAVS1 sites. The HSV/AAV amplicon vectors will be injected intravenously into adult and neonatal Atm -/- AAVS1 +/+ mice, and into the cerebellum of adult mice to evaluate integration events in neural cells. The long-term goal of these studies is to explore means of therapy for A-T, which could be translated into clinical trials and should be applicable to other neurologic diseases in humans.Narrative: This proposal focuses on achieving targeted gene therapy for ataxia-telangiectasia (A-T) mediated by an HSV/AAV hybrid amplicon vector. The long-term goal of these studies is to explore means of therapy for A-T, which could be translated into clinical trials and should be applicable to other neurologic diseases in humans.